Karyotype Stability and Genome‐Specific Nucleolar Dominance in Peanut, Its Wild 4× Ancestor, and a Synthetic AABB Polyploid

Abstract

Allopolyploidy is a significant evolutionary process involved in the origin of many crops, including peanut (Arachis hypogaea L.). The process usually results in a series of chromosome, genomic and epigenetic rearrangements in the derived polyploids. Here, we examined the chromosomal consequences undergone by AABB tetraploids of Arachis after the genome merger. For that objective, different chromosome markers and DNA contents were compared among peanut, its wild tetraploid ancestor, and the diploid genome donors A. duranensis Krapov. & W.C. Gregory (AA, female) and A. ipaënsis Krapov. & W.C. Gregory (BB, male). The analysis also included an artificially synthesized allotetraploid using A. ipaënsis as a female [(A. ipaënsis × A. duranensis)4×]. The karyotypes in the natural (originated ~10,000 yr ago) and newly synthesized allopolyploids have largely maintained the patterns of heterochromatin and ribosomal RNA loci detected in the diploid progenitors. Intergenomic translocations were not evident using genome in situ hybridization, and the DNA contents of the allotetraploids corresponded to the expected sum of those observed in their parental species. The analysis of ribosomal DNA loci and their association with nucleolar organizing regions revealed a rapid establishment of nucleolar dominance in favor of the A genome. The large macrostructural stability of karyotype observed here after polyploidization has not been frequently cited for polyploid crop plants. This stability is significant for peanut breeding, since it suggests that effective introgression of wild useful alleles into cultivated peanut may potentially occur in most of the extension of the A and B chromosome complements.

Occurrence of 2n microspore production in diploid interspecific hybrids between the wild parental species of peanut (Arachis hypogaea L., Leguminosae) and its relevance in the genetic origin of the cultigen

“…Currently, cytogenetic, phylogenetic, and molecular evidence indicate that the wild species involved in the origin of peanut are A. duranensis and A. ipaënsis (Bertioli et al., 2016; Grabiele et al., 2012; Kochert et al., 1996; Moretzsohn et al., 2013; Robledo et al., 2009; Seijo et al., 2007). Recent research has also established that A. hypogaea is a segmental allotetraploid, and that the six botanical varieties of the crop, as well as the immediate wild antecessor A. monticola , have suffered a single event of polyploid origin, involving A. duranensis as the female parent and A. ipaënsis as the male parent (Bertioli et al., 2019; Grabiele et al., 2012; Seijo et al., 2007, 2018). It has been hypothesized that the probable center of origin of A. hypogaea was the south of Bolivia and northwest of Argentina, which is the current distribution area of the diploid species involved in its origin (Dillehay, Rossen, Andres, & Williams, 2007; Grabiele et al., 2012; Krapovickas & Gregory, 1994; Simpson, 2001).…”

Transference of multiple resistance to peanut through the development of cross-compatible complex hybrids of wild Arachis

“…Hybridization and polyploidy usually have been reported as processes that induce genomic and epigenetic rearrangements (Chen, 2007;Madlung and Wendel, 2013). Only few allopolyploids remain as examples that have not undergone conspicuous chromosome rearrangements, among them is A. hypogaea (Seijo et al, 2018). The sum of chromo-some markers here analyzed by FISH revealed that the complex amphidiploids showed a high stability in their karyotypes.…”

The role of microRNAs in responses to drought and heat stress in peanut (Arachis hypogaea)

“…Focusing on the subgenome‐preferential expression of identified (Supporting Information S11; Tables S2 and S4) and validated miRNA target gene homoeologues and effectors in different tissue types (root, stem, flower, leaf, pods, and pegs), over short‐term time course treatments, and in wild relatives (Vinson et al., 2018; Yin et al., 2018) may reveal the adaptive nature of allopolyploid miRNA target gene losses and expression changes common to legumes. Further work is required to reveal the evolutionary innovations of MIRNA s in stress responses and nodulation (De Luis et al., 2012), and the roles of sRNAs in epigenetics of heat stress memory and male fertility (Bilichak & Kovalchuk, 2016; Malik & Zhao, 2022; Ramakrishnan et al., 2022), nucleolar dominance, genomic maintenance, and stability (Seijo et al., 2018). Such knowledge of sRNA functions can be applied to harness the genetic diversity of wild Arachis species to accelerate molecular breeding for value‐added agronomic traits.…”